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<p>The present study investigates the complex interplay of size, shape, and loading surface on the uniaxial compressive strength (UCS) of marble, a prevalent material in construction and decoration. From the Nikanai Ghar Formation (District Buner, Pakistan), selected marble samples were prepared into cylindrical and prismatic specimens with varying geometries (height-to-diameter or width ratios of 0.5, 1.0, 2.0, 3.0, and 3.0) and cross-sectional shapes (circle, square, rectangle). Comprehensive testing—including Schmidt hammer hardness, ultrasonic pulse velocity (UPV), specific gravity, water absorption, and UCS measurements—revealed the complex interactions between these variables. For the shape effect, UCS consistently decreased with increasing height-to-diameter (<i>H</i>/<i>D</i>) or height-to-width (<i>H</i>/<i>W</i>) ratios for all shapes, reaching a plateau at approximately ratio = 2.0. Square specimens exhibited the highest UCS across all <i>H</i>/<i>W</i> ratios (ranging from 69.1 MPa at <i>H</i>/<i>W</i> = 1.0 to 56.2 MPa at <i>H</i>/<i>W</i> = 3.0), exceeding both cylindrical and rectangular counterparts by up to 20%. Likewise, for the size effect, UCS displayed an inverse relationship with specimen diameter/width: The smallest circular specimens (42 mm diameter) achieved the highest UCS (43.7 MPa), while the largest square specimens (100 mm side) showed the lowest UCS (29.0 MPa). This size effect became less pronounced beyond ~ 70 mm specimen size. Square cross sections consistently yielded higher UCS than circular or rectangular specimens of comparable size and slenderness, suggesting that loading surface geometry plays a significant role in strength behavior. These findings challenge current testing standards. Our results suggest that the International Society for Rock Mechanics (ISRM) recommended slenderness of <i>H</i>/<i>D</i> (or <i>H</i>/<i>W</i>) ≥ 2.5 produces more reliable UCS values than the American Society for Testing and Materials (ASTM) recommendation of ≥ 2.0. Additionally, incorporating specimen loading surface geometry into testing standards could refine rock strength evaluation techniques. </p>

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Investigating the Scale Effect on the Compressive Strength of Marble: Influence of Specimen Size, Shape, and Loading Surfaces

  • 期刊论文

  • 发表日期：

    2025年6月24日

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  • Adnan Qadir,
  • Waqas Ahmed,
  • Muhammad Yasir,
  • Ihtisham Islam,
  • Abdul Rahim Asif,
  • Salman Ahmed Khattak

摘要

The present study investigates the complex interplay of size, shape, and loading surface on the uniaxial compressive strength (UCS) of marble, a prevalent material in construction and decoration. From the Nikanai Ghar Formation (District Buner, Pakistan), selected marble samples were prepared into cylindrical and prismatic specimens with varying geometries (height-to-diameter or width ratios of 0.5, 1.0, 2.0, 3.0, and 3.0) and cross-sectional shapes (circle, square, rectangle). Comprehensive testing—including Schmidt hammer hardness, ultrasonic pulse velocity (UPV), specific gravity, water absorption, and UCS measurements—revealed the complex interactions between these variables. For the shape effect, UCS consistently decreased with increasing height-to-diameter (H/D) or height-to-width (H/W) ratios for all shapes, reaching a plateau at approximately ratio = 2.0. Square specimens exhibited the highest UCS across all H/W ratios (ranging from 69.1 MPa at H/W = 1.0 to 56.2 MPa at H/W = 3.0), exceeding both cylindrical and rectangular counterparts by up to 20%. Likewise, for the size effect, UCS displayed an inverse relationship with specimen diameter/width: The smallest circular specimens (42 mm diameter) achieved the highest UCS (43.7 MPa), while the largest square specimens (100 mm side) showed the lowest UCS (29.0 MPa). This size effect became less pronounced beyond ~ 70 mm specimen size. Square cross sections consistently yielded higher UCS than circular or rectangular specimens of comparable size and slenderness, suggesting that loading surface geometry plays a significant role in strength behavior. These findings challenge current testing standards. Our results suggest that the International Society for Rock Mechanics (ISRM) recommended slenderness of H/D (or H/W) ≥ 2.5 produces more reliable UCS values than the American Society for Testing and Materials (ASTM) recommendation of ≥ 2.0. Additionally, incorporating specimen loading surface geometry into testing standards could refine rock strength evaluation techniques.